Download PACS 535-14 G. I. Kropotov, E. V. Tsygankova TYDEX: OPTICS

PACS 535-14
G. I. Kropotov, E. V. Tsygankova
TYDEX, J.S.Co.
Domostroitelnaya str. 16, 194292 St. Petersburg, Russia
E-mail: [email protected]
TYDEX: OPTICS FOR THz PHOTONICS
TYDEX offers a wide range of optics for THz photonics: passive components (lenses, windows, prisms, mirrors, spectral and beam splitters, and waveplates), built up components (low pass and band pass filters, polarizers, and attenuators),
and devices (Golay detectors).
Keywords: AR coating, THz lenses, THz windows, THz prisms, THz mirrors, THz spectral and beam splitters, THz
waveplates, THz low pass and band pass filters, THz polarizers, THz attenuators, Golay detectors.
Г. И. Кропотов, Е. В. Цыганкова
ТИДЕКС: ОПТИКА ДЛЯ ТГц ФОТОНИКИ
ТИДЕКС предлагает широкий диапазон оптики для ТГц фотоники: пассивные компоненты (линзы, окна,
призмы, зеркала, светоделители, спектральные делители, волновые пластинки), сборные компоненты (фильтры
нижних частот, полосовые резонансные фильтры, поляризаторы, аттенюаторы) и устройства (детекторы Голея).
Ключевые слова: просветляющие покрытия, ТГц линзы, ТГц окна, ТГц призмы, ТГц зеркала, ТГц лучеделители, ТГц спектральные делители, ТГц волновые пластинки, ТГц фильтры нижних частот, ТГц полососовые резонансные фильтры, ТГц поляризаторы, ТГц аттенюаторы, детекторы Голея.
Introduction
Nowadays interest to THz radiation is growing fast. Many different disciplines such as ultra fast spectroscopy, semiconductor device
fabrication, and bio-medical imaging involve
the recent development of THz technology. The
THz research activities have mainly focused on
generation and detection until lately, but the
focal point has shifted to the practical applications such as high-speed communication, molecular spectroscopy, security imaging, and medical diagnosis, among many others [1].
Research and industrial applications require
availability of good tool base. To satisfy needs
of THz photonics TYDEX develops and produces a wide range of optics. Offered products
can be divided into three groups:
- Passive components (lenses, windows,
prisms, mirrors, spectral and beam splitters, and
waveplates);
- Built up components (low pass and band
pass filters, polarizers, and attenuators);
- Devices (Golay Detectors).
Crystalline materials (high-resistivity float
zone silicon (HRFZ-Si), crystal quartz and sapphire) as well as polymer ones (polymethylpentene (TPX) and high-density polyethylene
(HDPE)) are used for components manufacturing. Organic materials have uniform stable
transmission about 80-90% starting from
~200 µm and to 1000 µm and more. It should
be noted that TPX is optically transparent in
UV, visible, and THz ranges, what allows using
a HeNe laser beam for alignment. Crystalline
materials have lower transmission in THz range
due to reflection losses. For silicon it is 50-54%
starting from 50 µm, for quartz it is >70% starting from about 120 µm, for sapphire it is >50%
starting from about 350 µm at 1-2 mm sample
thickness.
1. Passive components
TYDEX offers lenses of different shapes.
Meniscus, hyper-/hypo-/hemispherical, bullet,
and plano-cylindrical lenses are made of
HRFZ-Si and plano-convex and bi-convex
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Vestnik Novosibirsk State University. Series: Physics. 2010. Volume 5, issue 4
© G. I. Kropotov, E. V. Tsygankova, 2010
“‡„ˆӂ‡ˇ Í‚‡ÁËÓÔÚË͇
Terahertz Quasi-Optics
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lenses – of TPX. AR coating of hemispherical
HRFZ-Si lenses is possible. One-sided (spherical surface) AR coating increases transmission
of the lens by 30 relative percents in comparison with transmission of uncoated lens in specified range.
Windows (plano-plano and wedged) are
produced of any material mentioned above. AR
coating of HRFZ-Si windows is offered.
Transmission of two-sided AR coated window
is increased up to 90 % in specified range.
TYDEX manufactures HRFZ-Si prisms of
the following configurations: right angle and
attenuated total reflectance (ATR) ones. Right
angle prisms are used in optical schemes. ATR
prisms allow investigating materials which are
difficult to analyze in transmission.
Also TYDEX produces NIR- and MIR-THz
spectral splitters (HRFZ-Si and crystal quartz
substrates). NIR-THz splitter is used for separation of pump radiation (center wavelength is
790–800 nm) from THz radiation in
Ti:Sapphire laser and MIR-THz splitter –
for separation of pump radiation (9.6 µm and
10.6 µm) from THz radiation in THz laser optically pumped by CO2-laser.
There are two types of HRFZ-Si beam splitter we supply. The first one is singlepass beam
splitter with transmission/reflection ratio
~54%/46%. It is used in optical schemes where
radiation passes through beam splitter one time.
In fact, plano-plano HRFZ-Si window could be
used as singlepass beam splitter. The second
Fig. 1. Transmission spectrum
of low pass filter with blocking
wavelength 21 µm
type of beam splitter is used in Michelson interferometer scheme where beam passes through
splitter several times. Beam splitter for Michelson interferometer as opposed to conventional
beam splitter is produced with very high degree
of accuracy.
Gold coated mirrors (quartz glass substrate)
for full reflection of THz beam are offered too.
TYDEX supplies monochromatic λ/2
and λ/4 crystal quartz waveplates for different
operating wavelengths in the range of 35 to
1000 µm.
2. Built up components
Besides passive THz components TYDEX
manufactures low pass and band pass filters,
polarizers and attenuators.
THz low pass filters are intended to block
short wavelengths and transmit THz radiation
from MIR to MM. Standard cutting wavelengths are the following: 13 µm, 21 µm,
27.5 µm, 34 µm, 55 µm, 70 µm, 75 µm, and
94 µm. The filter is a set of materials mounted
in a holder with a fit ring. Action principle of
the filter is based on redistribution of radiation
by means of dispersion, reflection, scattering,
diffusion, diffraction, and interference. These
filters have high transmittance (up to 95%) in
pass range and low transmittance (<0.1%)
in suppression range. Example of transmission spectrum of low pass filter is shown
below.
Kropotov G. I., Tsygankova E. V. TYDEX: Optics for THz Photonics
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115
Fig. 2. Transmission spectra of
band pass filters with central
wavelengths 30 µm, 100 µm,
200 µm, 305 µm and 620 µm
Fig. 3. Transmission spectra of
THz attenuator elements
THz band pass filters are intended to transmit the wavelengths in the range of 20 µm to
1000 µm. The filters are fabricated from thin
metal foil with holes. Required central wavelength is defined by geometry of the holes and
can be any in above mentioned range. These
filters settle the problems of quasi-optical filtration of radiation in THz range. They also permit to get high degree of monochromatization
while aperture ration of device is also high. It is
worth using band pass filters when it is important to have high spectral resolution with high
aperture ratio as well as small overall dimensions and weight of device. Transmission of
such filters at maximum is 65-90% and transmission at suppression range is <4%. Trans-
mission spectra of five band pass filters are
shown below. The filters are supplied in holders.
To polarize radiation from 7 µm to MM
waves TYDEX offers polyethylene polarizers.
They are the sort of diffraction gratings. The
polarizer grating is made by forming grooves of
a triangle profile on the substrate (HDPE) and
subsequent deposition of a metal coating (aluminum) on one of the groove facets. The polarizers are supplied in holders (protective ring
with marked grid direction).
Variable wheel accessory is used for attenuation of high-power THz radiation (40 µm ÷
>1000 µm). It consists of 5 wheels. Four
wheels contain wedged metalized silicon wa-
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Terahertz Quasi-Optics
116
fers with different attenuation levels and one
wheel is empty. If necessary empty wheel can
be filled with custom element (e.g. filter). The
four attenuators have transmission 30%, 10%,
3%, and 1%. Their transmission curves (noise
is smoothed) are shown below. These attenuator elements can be used as single attenuators
or in combination that allows achieving different levels of attenuation (from 30% to 0.001%).
3.
Devices
Also TYDEX supplies one of the most efficient detecting devices - Golay Cell. It has excellent sensitivity at room temperature and flat
optical response over a wide wavelength range.
Three models of Golay Cells are available:
- GC-1P - Golay Detector with HDPE window is intended for monitoring and control of
MIR and THz radiation;
- GC-1T - Golay Detector with TPX window – for operating with UV-NIR and THz
radiation;
- GC-1D - Golay Detector with Diamond
window – for usage of VIS-THz radiation.
Golay detectors are manufactured in-house
and calibrated individually. Delivery includes a
detector head and a power supply unit. A
mount for the filters and low pass filters can be
supplied as an option.
Other THz built up components and devices
are in progress.
References
1. Yun-Shik Lee, Principles of Terahertz
Science and Technology // Springer
Science+Business Media, LLC. 2009. Preface.
15.09.2010